Many conventional trench shields had been disclosed for protecting side walls of a trench excavation against collapse. However, they are complex in structure and not mobile in the trench, thereby being inconvenient for use in a construction site especially in a pipe construction work.
U.S. Pat. No. 5,306,103 to Spencer disclosed a wheeled carriage assembly for trench shield having protective panels (18) hung on an axle members (30) of a plurality of wheels (52) which are rolling on a ground surface (22) adjacent the trench. Such a wheeled carriage assembly may suspend and support a trench shield for advancement along an excavated trench such as for laying a pipe (16) in the trench.
However, such a prior art (U.S. Pat. No. 5,306,103) has the following drawbacks:
1. The total weight of the trench shield is loaded and focused on the wheels (52) which are supported on the ground surface very near the trench excavation (14). The ground surface soil between the wheel (52) and the trench excavation (14) is so weak and may be vulnerably collapsed especially when subjected to the heavy pressure caused by the trench shield. PA0 2. For adjusting the spacing of the two panels (18) along the axle (30) of the wheels, the heavy weight of the shield as suspended on the axle (30) will cause friction between the brackets (40) and the axle (30), thereby increasing the adjustment difficulty. PA0 3. The ground surface adjacent the trench excavation may be piled or placed with excavated materials, soil or stones to cause corrugated or uneven ground surface, thereby obstructing the rolling of the wheels and influencing the forward movement of the trench shield.
The present inventors have found the drawbacks of the conventional trench shields and invented the present trench shield easily constructed and conveniently moved in a trench excavation.